Fibrous bodies and method and apparatus for producing same

ABSTRACT

A fibrous body which includes at least two layers of strands of continuous filaments and binder particles in each layer. One of the layers has filaments of the strands therein at least partially dispersed to form a mesh size which entraps binder particles therein which have a mesh size larger than the mesh size of the dispersed filament layer, as well as smaller size particles lodged at intersections and crossovers. Another layer has strands which form a mesh size which do not necessarily entrap binder particles but may retain particles therein at interstices of strands. The fibrous body has a binder content in the dispersed filament layer which is larger per unit volume than the binder content of the other layer. Preferably a plurality of successive layers of continuous multi-filament strands are deposited on a collecting surface in a mat-like mass. Binder particles are distributed throughout the mat-like mass, the binder particles having a mesh size with respect to the mesh size of the layers which enable circulation of the binder particles throughout the mat-like mass. The strands in one of the layers are opended to separate the filaments of the strands from each other and change the mesh size of that layer to mechanically entrap binder particles therein. The excess binder particles are removed from the mat-like mass to provide a first layer with a higher percentage binder content than the remaining layer or layers in the mat-like mass.

This is a division of application Ser. No. 233,549, filed Mar. 10, 1972,now abandoned.

BACKGROUND OF THE INVENTION

This invention relates to fibrous bodies, to the manufacture of fibrousbodies, and to methods of applying binders to fibrous products; and moreparticularly to methods of distributing binders in such products. Morespecifically, the invention relates to a process for bondingmulti-filament strands in a body of desired form, in which the filamentsare of fibrous glass and are gathered into strands immediatelysubsequent to the filament forming operation, the strands then beingcollected and arranged in a body.

Mats of fibrous glass, because of the inherent glass properties,especially those of strength and inertness, have many uses. They havebeen employed as filtering, acoustical and thermal insulating media.They also serve effectively for roofing sheets, nonwoven fabrics, andfor reinforcing plastic products such as electrical grade laminates.

In some instances, the mats are composed of short fibers held togetherby a binder. In others the mats are bonded webs of chopped fibrous glassstrands. Bundles or strands of continuous glass filaments have also beendisposed in mat form. Strands of filaments have superior strengthbecause of the continuous nature of the filaments and their concentratedlinear association in strant form. Accordingly, fibrous glass strandsare a most desirable constituent where strength is a primeconsideration.

Various resinous materials including dispersions, emulsions, solutions,and dry granular powders have been applied to fibrous glass masses asbonding materials to give the finished products dimensional stabilityand strength. Such liquids or powdered resins have been added in variousways such as by wiping, spraying, submersion and dusting. Obtaining adesired distribution of binding material in the mat at a reasonable costhas posed a problem which has been approached in the prior art in avariety of different ways.

A commonly employed method has been to spray a water dispersion orsuspension of the resinous material upon the fibrous glass immediatelyadjacent the fiber forming operation. This method provides a mat orother body, in which the fibers are massed, having fairly uniform binderdistribution and good strength. However, an excessive amount of water isinvolved and it is necessary to drive off through heating a majorportion of this water. The heating requires considerable time and isotherwise costly from a production standpoint.

The same problem of a high water content is faced when a liquid binderis applied by spraying or by dipping to a mat of chopped strands orcontinuous strands.

Another former method has been to submit the mat of fibers to ascattering of a powdered resinous material. This granular binder hasbeen necessarily shaken down into the mat by vibration and later set byapplication of heat. In some instances it is necessary to tear the matapart to mix the resin particles. The mats so treated tend to havepoorly bonded areas reducing tensile strength, and high ignition losses,indicating nonuniform distribution and an excessive binder component.

There has also been introduced to the art in U.S. Pat. No. 3,318,746,issued May 9, 1967, and in Canadian Pat. No. 756,563, issued Apr. 11,1967, two methods for overcoming the high water content problem andobtaining substantially uniform distribution of the binder throughoutthe mat-like mass.

In U.S. Pat. No. 3,318,746, a liquid binder is first appliedlongitudinally to the individual filaments before they are gathered intostrand form. The strands are then collected in a body of desiredconfiguration such as a mat and the liquid binder in the body is driedin a graduated manner whereby the binder adjacent one surface iscomparatively dry and the opposite surface is comparatively wet. Apowdered binder is directed against the comparatively dry surface andtoward the comparatively wet surface. The powdered binder is distributedand retained substantially uniformly through the body due to theincreasing proportion of the binder caught by the progressively wetterportions while the amount of binder decreases through the progressiveretention of the binder particles as they pass through the drierportions of the body. Thus there is a substantially uniform distributionof binder in the mat without having an excessive amount of moistureretained in the mat which must be driven off when the binder is beingcured.

In the Canadian Pat. No. 756,563, a mat of randomly oriented glassstrands is formed on a foraminous conveyor. A water dispersion of solidresin particles is flowed through the mat on the foraminous conveyor toleave resin particles distributed throughout the mat. After the waterdispersion of binder particles is passed through the mat, the conveyorpasses over a suction box which sucks excess liquid from the conveyorand the mat. The mat, with the small amount of water left therein in theform of droplets, is passed through an oven to reduce the droplets insize and bring the particles of resin in around the area of contactbetween the fibers to bridge the fibers at the point of contact. Again asubstantially uniform distribution of binder has been obtained withoutan excessive amount of water being left in the mat which must be drivenoff before the binder can be cured.

The above and other methods not mentioned herein are now being used toachieve substantially uniform distribution of binder throughout theentire fibrous body, but we have discovered that improvedcharacteristics for certain applications can be achieved by selectivelydistributing binder throughout a mat-like mass of strands. Thedistribution is uniform in each of at least two different areas, but thebinder percentage content or amount of binder solids of each area isdifferent. Mats of fibrous bodies used, for example, as reinforcement inthe manufacture of electrical grade laminates, perform better when thereis a concentration of or a higher percentage binder content adjacent toat least one surface of a mat or mats used for reinforcement of thelaminates.

The dielectric strength, dielectric constant, dielectric breakdown andarc resistance, and dissipation factors of an electrical grade laminatemade from such reinforcing mats are substantially improved over suchlaminates made from mats having a binder solids content which is uniformthroughout the thickness thereof and which do not have one or more atleast partially filamentized layers. Moreover, the distribution ofbinder and filamentization of strands as described improves thehandleability, unrollability, and the strength of such mats. Theseimprovements have been obtained in the above-described product whilestill enabling a reduction of fifty percent in the amount of bindersolids required to attain the improved properties.

None of the hereinbefore described methods or other known methods forapplying binders to fibrous products will permit a high degree ofcontrolled or selective distribution of binder in a mat-like mass toobtain one layer which has a higher percentage binder content than oneor more other layers also included in the mat. We have discovered that apreferred method for making a mat having the desired improvedcharacteristics includes the steps of manufacturing a multi-layer mat inwhich at least one of the layers has strands with a different number offilaments to provide a faster reopening capability than the other layeror layers in the mat. Even with the preferred method of manufacturingthe mat, however, none of the known methods of binder distribution wouldselectively distribute the binder as desired.

Multi-layer strand mats by themselves are not new to the art, havingbeen introduced, for example, in U.S. Pat. No. 3,442,751, issued May 6,1969. However, there has been no appreciation of the improvedcharacteristics than may be obtained in the product of this invention,nor any attempt to selectively distribute binder throughout the mat toobtain a higher percentage binder content in one or more of the layersof the multi-layer mats than is present in other layers.

It was further discovered that it is possible to filamentize or open thestrands in one layer, or less than all the layers, of the multi-layermat in place, preferably on a collection surface. This novel method ofselectively filamentizing strands of a mat and the apparatus forcarrying out the method is used to entrap or retain more binderparticles in the resulting changed mesh size of a filamentized layertherefrom to provide a higher bond percentage binder content in thatlayer than in the remaining portion of the mat.

In a co-pending application Ser. No. 201,002, files Nov. 22, 1971, nowU.S. Pat. No. 3,760,458 and assigned to the same assignee as the presentinvention, there is disclosed a method for filamentizing or reopeningthe strands in the entire body of a mat-like mass or collection ofstrands to filamentize all of the strands in the body to provide auniform dispersion of filaments to achieve a more uniform porosity andintegrity throughout the entire mat. This process, however, distributesbinder uniformly throughout the mat and does not consider a method forselectively distributing the binder in the mat to obtain a higherpercentage binder content in individual layers thereof and the productdoes not provide the unique characteristics of the product disclosedherein.

Accordingly, it is an object of this invention to provide a new methodand apparatus for producing a novel fibrous body which advantageouslymay have binder selectively distributed therein to obtain a higherpercentage binder concentration in a predetermined portion of the mat.

It is another object of this invention to provide a new and improvedmethod and apparatus for selectively distributing particles of a solidbinder material throughout a mat of glass fibers.

Still another object of the invention is the provision of new andimproved method and apparatus for applying binder to mats in such amanner that the handleability of the mats will be improved over that ofthe prior art processing, in which the performance of an objectreinforced by such a mat is improved over prior art products, and to usea smaller amount of binder to accomplish the above objectives than hasbeen used heretofore.

It is still further object of this invention to provide improved fibrousbodies which enhance the physical, mechanical and electrical propertiesof a composite moled laminate or structure using the fibrous bodies forreinforcement, and to provide an improved laminate product and a novelprocess for making same.

Another object is the provision of an improved continuous process andapparatus for economically producing bodies of fibrous glass.

SUMMARY OF THE INVENTION

The above objects and the principles of the invention are illustratedand featured in a preferred apparatus for continuously producing fibrousbodies comprised of continuous glass strands. A mat-like mass ofmulti-filament strands is continuously provided in an unwoven form on amoving surface. The mat-like mass on the moving surface is flooded witha strand dispersing medium which may carry binder particles insuspension, a liquid binder as an emulsion, or both. The stranddispersing medium is flooded onto the mat-like mass by guiding themoving surface past a flooding medium supply station. If binderparticles are carried by the medium they have a mesh size which enablesdistribution of the particles throughout the mat-like mass by the liquidcarrier as the mat-like mass is flooded. Similarly, a liquid binder isdistributed throughout the mat-like mass by the medium.

Binder is continuously added to the mat-like mass as it moves past theflooding suspension supply station at a rate to create stream flow inthe same direction with and at substantially the same rate of movementas the mat-like mass on th moving surface. The mat-like mass ismaintained in the flood stream for a soaking interval which issufficient to enable the strand dispersing medium or phase of the floodliquid to substantially overcome the forces holding the filamentstogether in strand form.

The flooded and upper portion of the mat-like mass is impinged with asecond supply of the strand dispersing medium at the end of the soakinginterval to mechanically aid in dispersing the filaments in the upperportion of the mat-like mass. The mesh size of the upper portion of themat-like mass is thus changed by increasing the number of interstices toenable retention or entrapment of binder particles in the upper portionof the mat-like mass. The increased number of interstices and surfaceareas resulting from partial or full filamentization provides moredeposit areas for binder, so that more binder may be retained in thefilamentized layer.

Excess binder, and liquid dispersant are removed from the mat-like massafter impingement of the upper surface thereof and before the filamentsof the strands in the lower portion disperse to change the mesh size ofthe lower portion to a value which would prevent or inhibit binderparticle movement therethrough or would provide added surface area fordeposition of binder thereon. This enables the upper portion to retain agreater percentage of binder particles than the lower portion of themat-like mass.

The mat-like mass is preferably provided on the moving surface bysuccessively depositing a plurality of layers of multi-filament strandson the moving surface. The multi-filament strands in the uppermost layerof the preferred embodiment are advantageously formed in a manner whichenables a more rapid reopening of the filaments in the strands, inresponse to contact with a strand dispersing medium. This more rapidreopening capability of the filaments in the strands in the uppermostlayer insures more particle entrapment by or increased surface area inthe uppermost layer while enabling binder to be removed from the lowerportion of the mat-like mass before filamentization or reopening of thelower portion strands.

In the preferred embodiment of the invention the strands in the upperportion of the mat-like mass are formed with fewer filaments per strandthan the strands in the lower portion of the mat-like mass to enable amore rapid reopening of the upper portion strands than the strandsadjacent to the upper portion. Advantageously, more of the fewerfilament strands per unit area are deposited in the upper portion of themat-like mass adjacent the upper portion, thus forming more smallerinterstices in the upper portion and a better binder retentioncapability.

The filaments are advantageously directly deposited on the collectingsurface by attenuating filaments from molten streams of glass, applyinga forming size to the filaments which may include a coupling agent (toenhance the bond between the glass filaments and the resin the fibrousmat may later be combined with), and gathering the filaments into aplurality of multi-filament glass fiber strands.

In the preferred embodiment the upper layer of the mat-like mass isformed from multi-filamant strands having a first predetermined numberof filaments in each strand while the mat-like mass below and adjacentto the upper layer is formed with multi-filament strands having aboutfifty percent more filaments per strand than the strands in the upperlayer. The smaller strands have the capability of reopening more quicklyin response to contact with the strand dispersing medium to enable amesh size change to retain binder before the filaments of the largerstrands of the lower layer disperse to inhibit passage of binder throughthe lower layer. It was also found advantageous in the preferredembodiment to provide approximately 50 percent more of the smallerstrands per unit area in the upper layer, thus enabling the smallerstrands to lie closer together to form smaller interstices to enhancethe binder retention capability of the upper layer.

The suspension removal step advantageously includes positively forcingair through the mat-like mass at a pressure which reduces the moisturecontent of the mat-like mass to approximately the same weight as thefilaments and strands in the mat-like mass, before the mat-like mass ispassed through an oven to flow, set and cure the binder and integratethe mass into a substantially unitary body. It is also advantageous toprevent flow out through the edges of the mat-like mass during theflooding and extraction or removal steps to maintain a substantiallyuniform binder distribution horizontally, within the upper and lowerportions of the mat-like mass, and to prevent strand and filamentmovement transversely in response to edge flow. Edge flow prevention ispreferably accomplished by dimensionally controlling the width of themat-like mass by providing spaced elements above the moving conveyorsurface to limit the width of the mat and to channel flood stream flowwith the mat.

In the preferred embodiment of the invention the combined binder-mediumwhich is flooded onto the mat-like mass comprises a suspension of solid,resinous binder particles in a liquid strand dispersing phase, medium orcarrier. Of the total weight of binder and dispersing medium, 95 to99.9% by weight can be the liquid strand dispersing phase and 0.1 to 5%by weight can be the binder particles.

The liquid strand dispersing phase of the binder is cheifly composed ofwater. However another preferable component is any compound, such as aresin emulsion or liquid resin which is dispersible in water and willform a sticky, tacky or glue-like layer or film on the filaments orstrands of the mat-like mass. This film helps hold the solid binderparticles onto the filaments or strands. Polyester, phenolic, epoxy,vinyl acetate, urethane or other similar resins or emulsions can beused. Generally a resin is chosen to either match to be compatible withthe resin the mat-like mass will be combined with to make a laminate orother product. This layer or film should be tacky enough to retain atleast 80% of the solid resin particles coming in contact with it afterexcess binder has been drained off. Below 80% retention the mat-likemass may have too many loose or unbonded filaments or strands andpresent a fuzzy surface. In some product applications, for example,electrical laminates or pultruded shapes such as channels, this could behighly undesirable.

Other components of a preferred liquid strand dispersing phase aregenerally a catalyst and a coupling agent. If a resin or resin emulsionis used the catalyst promotes cure (polymerization) of the resin orresin emulsion of dispersion in the curing oven. The coupling agentserves to enhance the chemcal bonding of the strands and filaments tothe laminating or other type of resin later combined with the mat-likemass.

By weight of the solids content of the entire preferred liquid phase ofthe binder, the catalyst will comprise about 0.5 to 2% and the couplingagent about 20 to 50% and the resin about 50 to 80%. By weight of thetotal liquid phase, the total solids content should be about 0.1 to 3%and preferably about 0.25%.

The solid resin particles which are suspended in the liquid phase bondthe filaments and strands to one another after they are heated in anover and thereby caused to melt, flow around the filaments and strands,and then set. This is the case if the particles are made of athermosetting resin. If a thermoplastic resin is used the particleswould set outside the heated oven.

The binder particles can be held in the mat-like mass (prior to meltingand flowing to bond the fibers) by being (a) lodged at filament orstrand crossover points, or (b) entrapped in one or more layers of themat-like mass where the filaments have been dispersed, or (c) held tofilaments or strands by the tacky film formed on the filaments andstrands.

In situations where only a small amount of binder particles are desiredin layers of the mat-like mass which do not have dispersed filaments, anumber of different approaches could individually or in combination beused. Only binder particles of a size that would be entrapped by thedispersed filaments could be used. Or the resin emulsion that puts atacky film on the filaments and strands could be left out of the liquiddispersing phase of the binder. This would cause far less binderparticles to be held to the filaments or strands, both along theirlength and at crossover points.

It is also possible to vary the liquid resin or resin emulsion componentof the binder formulation. For example if it is desired for some reasonto have the filaments and strands solely or primarily bonded to oneanother by a liquid binder, a suitable liquid bonding resin could bemixed with the liquid dispersing phase. Suitable bonding resins could bethose resins already mentioned as the resinous component of the liquiddispersing phase. In this instance the solids content of the liquidphase could be raised from the 0.1 to 3% by weight preferred range to 6to 20% by weight of the total liquid phase. In this instance no binderparticles or only those of a size that would be entrapped only orpreferentially in the filamentized layer or layers of the mat would beused. Generally a liquid binder is not used in making mats which areused to reinforce laminates or the like. This is because the liquidbonding resin puts such a heavy coating on the filaments and strandsthat the laminating or other resin being reinforced by it hinders thelaminating resin from bonding to the filament or strand surface.

To attain the best possible results with the mat-like mass made inaccordance with this invention the solid binder particles should rangein size from about 35 to 420 microns in diameter. This micron rangecorresponds to 40 to 400 mesh (U.S. Sieve Series).

The liquid strand dispensing phase of the binder can serve at leastthree functions. First, it can form a tacky, sticky or glue-like film onthe filaments and strands to hold or retain the binder particles ontothe filaments and strands; second, it can carry the binder particlesuniformly throughout the mat-like mass, and third, it can dispense thefilaments of the strands in one of the layers of the mat-like mass.

In one embodiment of the invention good results were obtained when thefilament diameters were approximately 68 to 70 hundred thousandths of aninch and about one-half of the binder particles were 150 microns indiameter or larger (150 to 420 microns) and the other half were smallerthan 150 microns in diameter (35 to 149 microns). When using the binderparticle size and the filament diameter size just described, a mat-likemass was produced which prior to soaking in the binder had openingsbetween strands of about 177 microns or 80 mesh. Thus the binderparticles smaller than 177 microns uniformly passed through or werecaught in the mat-like mass. After soaking in the binder however andopening the filaments in the upper layer of the mat-like mass, theopenings in the upper layer were reduced to about 150 microns or 100mesh. This layer then caught more binder resin particles (those between150 and 177 microns in diameter) and had a higher binder content thanthe other layer. A binder content of approximately 5 percent by weightwas found in the upper portion, and approximately 21/2 percent by weightin the lower portion. The ratio of the percentage of the upper portionto the percentage of the lower portion of the mat-like mass was suchthat the entire mat-like mass has an overall binder content of about31/2 percent by weight. However acceptable mats for electrical laminatesor pultruded shapes can have from one-half to 10 percent by weight ofbinder.

In the preferred method the product may further be provided with abottom-most layer in which the strands include fewer filaments perstrand than the strands in a layer which is adjacent to the upper layerand intermediate the upper and bottom layers. The bottom layer alsopreferably includes more strands per unit area than the intermediatelayer. When the product is being used in an application where a resinmatrix must rapidly gain entrance to the central body portion of the matthrough one of the surfaces, then it is preferred that the bottom layerof strands not be filamentized so that the matrix may be more easilyadmitted to the mat. However, the provision of more interstices doesretain more binder during the extraction of excess binder therethroughto increase the surface binder content to improve handleability of themat. For other applications, when an additional bottom layer isutilized, the flooding interval may be adjusted to overcome the forcesholding the lower layer filaments together in strand form sufficientlyto enable a dispersion of lower layer filaments in a manner to bedescribed hereinafter. Whichever method is used, there may be provided amat-like mass having upper and lower layers with higher percentagebinder contents than an intermediate layer.

There is further disclosed herein an improved method of manufacturing anelectrical grade laminate by preparing a fibrous mat so that at leastone outer face layer of strands of continuous filaments has a higherpercentage binder content than an adjacent inner layer of continuousfilament strands. If more than one of the fibrous mats are used, theyare positioned back-to-back so that the higher binder content layers ofeach mat face outwardly. The mats are impregnated with a resin matrixand are cured with pressure and heat to provide a solid laminate havingimproved punchability, dielectric strength, dielectric constant,dielectric breakdown and arc resistance, and dissipation factor. In apreferred embodiment the curing step included placing the impregnatedmats under 500 pounds per square inch of pressure with stops inserted tohold the press apart to achieve the desired thickness of the laminate,and holding the pressure for three minutes while maintaining theimpregnated mats at 235°F. The pressure was removed from the mats andtheir temperature was held at 150°F. for one hour, and then thetemperature was held at 200°F. for 2 hours.

Other objects, advantages, and features of this invention will becomeapparent when the following description is taken in conjunction with theaccompanying drawings, in which:

FIG. 1 is a side elevational view of a portion of a production lineincluding equipment adapted for the practice of the invention;

FIG. 2 is a somewhat enlarged vertical cross section of the productionline of FIG. 1 showing two pull wheels and associated apparatus forgathering filaments into strands and projecting the strands upon aconveyor;

FIG. 3 is a further enlarged side view of one of the wheels of FIG. 2receiving strands from a gathering shoe;

FIG. 4 is a front view on the same scale as FIG. 3, of the pulling wheelthere shown; and

FIG. 5 is a section of a preferred embodiment of the fibrous bodyconstructed according to the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to the drawings in more detail, the fibrous mat productionapparatus of FIG. 1 includes a portion of a series of molten glassfeeding bushings 21, depending from conventional glass melting tankswhich are not illustrated.

Continuous filaments 23 are drawn from the minute orifices of thebushings 21. For the purpose of being specific in describing theinvention in connection with this apparatus, it will be considered thatthere are 438 orifices in each bushing and the filaments drawn therefromhave an average diameter of 68 to 70 hundred thousandths of an inch.

A forming size is applied to the filaments as they pass over carbonapplicator rolls 24 of the conventional size applicators 25. If thefibrous mat is to be used as reinforcement in an electrical gradelaminate, a preferred composition of the forming size is shown in thefollowing Example 1.

EXAMPLE 1

                     % by weight                                                  Ingredient       of total size                                                ______________________________________                                        Weak Acid        0.01 to 0.10                                                 Lubricant        0.01 to 0.10                                                 Coupling Agent   0.10 to 2.0                                                  Water            remainder                                                    ______________________________________                                    

The lubricant is added to allow a pull wheel to attenuate filaments fromthe bushing without causing filament breakage. The lubricant used in theabove size formulation may be chosen from pelargonic acid-tetraethylenepentamine condensate solubilized with acetic acid or caprylicacid-tetraethylene pentamine condensate solubilized with acetic acid.Generally polyethylene glycol-monooleates or monostearates are useful aslubricants. So also are fatty acid-amine derivatives.

The coupling agents used are generally organo silicon (silane) or chromecoupling agents. Those silane coupling agents that may be used in thissize formulation are: gamma-methacryloxypropyltrimethoxysilane;gamma-aminopropyltrimethoxysilane; vinyl-tris(beta-methoxyethoxy)silane; and gamma-glycidoxypropyltrimethoxysilane. Other coupling agentstailored to the laminating or matrix resin later combined with the matcould also be used.

A weak acid such as acetic acid, lactic acid, citric acid or formic acidis also preferably added to the size when some silane coupling agentsare used to prevent the coupling agents from kicking out of thesolution. The acid is used in a quantity sufficient to keep the pH ofthe size on the acid side. Generally amino silanes, such asgamma-aminopropyltrimethoxysilane, will remain in solution in an acid orbasic solution.

Chrome coupling agents also may be used. These could be Werner complexcompounds in which the carboxylato group coordinated with the trivalentnuclear chromium atom contains an amino group or an epoxy group.

EXAMPLE 2

A specific size formulation found to give good results when a polyesterresin emulsion is used in the binder (as in Example 3) is as follows:

                            % by weight                                           Ingredient              of total size                                         ______________________________________                                        Galacial Acetic Acid    0.03                                                  pelargonic acid -                                                             tetraethylene pentamine condensate                                                                     0.030                                                caprylic acid -                                                               tetraethylene pentamine condensate                                                                    0.01                                                  gamma-methacrylocypropyltrimethoxysilane                                                              0.20                                                  Water                   remainder                                             The pH is kept 4.0 to 4.5.                                                    ______________________________________                                    

The filaments from each bushing, after the forming size is appliedthereto are grouped together to form a number of strands which areindividually segregated as they travel within grooves over therespective gathering shoes 27a, 27b illustrated in FIG. 1. The primarydivision of the filaments into strand groups may be accomplishedmanually at the start of production.

The showing of six bushing positions is representative of a 12 bushingproduction line apparatus to form the preferred embodiment of theproduct of this invention. The first two and the last two bushings ofthe series of 12 bushings deposit the bottom-most layers and top-mostlayers, respectively, of a mat 60 on collecting surface of a conveyor61. The filaments of each of the first two and the last two bushings arepreferably split or divided into 22 strands with approximately 20filaments per strand. The filaments of each of the intermediate ormiddle eight bushings are preferably split into 14 strands with 29 to 31filaments per strand.

The sets of strands 28 from the first two and the last two bushings inthe series pass down around grooved guide or aligning shoes and idlerwheels before being drawn over pulling wheels 35 and projecteddownwardly therefrom. Similarly, the sets of strands 29 from theremaining eight intermediate bushings reach pull wheels 36 and areprojected therefrom. The pull wheels are driven by motors 38 arranged inpairs between adjacent pull wheels longitudinally of the productionline.

The traction between the strands and the surface of a pull wheelfurnishes the pulling force that attenuates the glass filaments formedfrom the minute molten glass streams issuing from the orifices of thefurnace bushing. This adherence of the strands to the pull wheel isevidently due to the cohesive effect of the forming size carried by thestrands supplemented by other air and surface forces of attraction.

The strands projected from the pull wheels are deposited upon theforaminous conveyor 61 and accumulate to form a continuous mat 60. Theconveyor 61, or subsequent conveyors to which the mat 60 is transferred,carries the mat 60 through a selective binder application area to anoven 65 for curing of the binder components on the filaments and strandsof the mat. The cured mat 60 issuing from the oven 65 may have its edgestrimmed, be inspected and then packaged at a suitable packaging stationif immediate use of the mat product is not desired.

The binder which is flooded onto the mat-like mass of this invention cancomprise a suspension of solid, resinous binder particles in a liquidstrand dispersing phase, medium or carrier. Of the total weight ofbinder, 95 to 99.9% by weight can be the liquid strand dispersing phaseand 0.1 to 5% by weight can be the binder particles.

The liquid strand dispersing phase of the binder may be composedentirely of water. Another preferred component however is a resin orresin emulsion that is dispersible in water. Polyester, phenolic, epoxy,vinyl acetate or urethane resin emulsions can be used. Generally a waterdispersible resin or resin emulsion is chosen that matches or iscompatible with the resin that mat-like mass will be combined with tomake a laminate or other product.

The resin emulsion can be any resin that will form a sticky, tacky orglue-like coating, layer or film on the filaments or strands of themat-like mass. This film helps hold the solid binder particles onto thefilaments or strands. This is especially important during the shortperiod of time in the heated oven when the mat may have dried but thebinder particles have not yet melted and begun to flow. The resinemulsion layer or film should be tacky enough to retain at least 80% ofthe solid resin particles coming in contact with it after excess binderhas been drained off. Below 80% retention the mat-like mass may have toomany loose or unbonded filaments or strands and present a fuzzy surface.In sone product applications, for example, electrical laminates orpultruded shapes such as channels this could be highly undesirable.

Other components of the liquid strand dispersing phase are generally acatalyst and preferably a coupling agent. The catalyst is used topromote cure (polymerization) of the resin emulsion in the curing oven.The coupling agent serves to enhance the chemical bonding of the strandsand filaments to the laminating or other type of resin later combinedwith the mat-like mass.

The solids content of the liquid phase of the binder can comprise about0.5 to 2% catalyst, 20 to 50% coupling agent and about 50 to 80% resin.By weight of the total liquid phase, the total solids content can beabout 0.1 to 20%. Preferably when making mats for electrical laminatesthe total solids content should be about 0.1 to 3% and specificallyabout 0.25%. A formulation for the liquid phase or medium of the binderis shown in Example 3.

EXAMPLE 3

    Ingredient                % by weight                                         ______________________________________                                         Resin                                                                        Diethylene glyco-fumarate polyester                                           (70%) dissolved in diallyl phthalate (30%)                                                              0.30                                                 Catalyst                                                                     Benzoyl peroxide (50% solids) in a                                            butyl benzyl phthalate carrier                                                                            .0058                                              Weak Acid                                                                    Glacial Acetic Acid       0.03                                                 Coupling Agent                                                               gamma-methacryloxypropyltrimethoxysilane                                                                0.1                                                 Water                     remainder                                           ______________________________________                                    

The resin component in the liquid phase of the binder may be anythermosetting or thermoplastic resin which will give the tacky orglue-like characteristics outlined above. Examples of resin componentsthat can be used are polyvinyl acetate, vinyl toluene, diacetoneacrylimide, epoxy, phenolic, melamine, acrylic and urethane resins, aswell as the reaction products of propylene glycol and maleic ortrimellitic anhydride. Generally in electrical mats polyester resins areused.

A catalyst is chosen which will promote cure (polymerization) of theliquid resin during or after passage of the mat through a heating oven.When ethylene glycol fumarate or diethylene glyco-fumarate is used asthe liquid resin suitable catalysts are benzoyl peroxide, lauroylperoxide, stannic chloride pentahydrate, cobalt nitrate and the like.

A weak acid such as acetic, lactic, citric or formic acid may be addedto keep the pH of the liquid phase slightly acidic. This is onlynecessary when certain coupling agents are used in the formulation. Somecoupling agents have a tendency to kick out of solution in a neutral orbasic solutions, others do not.

The particular coupling agent used should be chosen to be reactive withthe resin that will eventually be combined with the mat to make aproduct. In Example 3 the coupling agent used works well with polyesterlaminating resins. Other coupling agents which could be used are mostsilane or chrome coupling agents. Those listed in the discussion of sizeformulations can also be used.

It should be noted that at the filament forming station, the filamentsreceive a coating of the forming size containing silane or couplingagent which tends to cover the entire surface of the filaments. Theremay be an occasional skip or bare spot devoid of a layer of the couplingagent. For this reason, it is believed preferable to also include acoupling agent in the binder to insure a continuous coating of silane inthose spots which might otherwise be bare or devoid of such material.

Also the binder coupling agent will coat the binder particles and againaid in the coupling of the matrix resin with the surfaces of the matfilaments and strands.

To attain the best possible results with the mat-like mass made inaccordance with this invention the solid binder particles should rangein size from about 35 to 420 microns in diameter. This micron rangecorresponds to 40 to 400 mesh (U.S. Sieve Series).

The binder particles circulated through the mat are both mechanicallyentrapped by the mesh size change in selected areas of the mat and alsoare attracted to and adhered to at least some of the filaments andstrands inall areas of the mat, including particles that are lodged inthe intersections or crossovers of strands or filaments in the portionsof the mat which do not have a mesh size change. When these particlesare heated in an oven they melt and flow around the strands or filamentsthey are in contact with or which are nearby and thereby bond thesestrands and filaments to one another. When the binder particles arepowdered thermosetting resins they set up and cure in the heated oven.When the are thermoplastic they melt and flow in the oven but set upoutside the oven at room temperature.

The binder particles should be of a chemical composition that iscompatible with or the same as the resin later combined with the mat tomake a product. Excellent results have been obtained by using particlesof ethylene glyco-fumarate suspended in the liquid phase of Example 3 inthe proportions shown in Example 4.

EXAMPLE 4

    Ingredient           Percent by Weight                                        ______________________________________                                        Example 3 liquid phase                                                                             99.85                                                    Ethylene glyco-fumarate particles                                             (35 to 420 microns in diameter)                                                                     0.15                                                    ______________________________________                                    

Binder particles preferably should have jagged, non-spherical orirregular surfaces. Smooth or spherical particles can too easily slipthrough filament or strand crossover points. Irregularly shapedparticles are more easily entrapped.

If the particles are thermosetting they should be able to melt, flow,set up and cure in a heated oven. It is of course important that theparticles flow before setting up. Generally they should melt below600°F. to be compatible with most mat making operations. If theparticles are thermoplastic they would set up outside of the oven.

In the vertical cross-section of FIG. 2 there is shown in elevation thefirst pair of bushings 21 of FIG. 1 and the apparatus associatedtherewith including the pull wheels 35 for depositing the strand on aconveyor. The pull wheels 35 with elements of the apparatus cooperatingtherewith are shown in enlarged form in FIGS. 3 and 4. As the wheels 35and their associated apparatus are quite identical in structure andfunction, the description of the wheels 35 will generally apply to theapparatus including wheels 36 for the intermediate bushings.

From the guide or aligning shoe 31, which is grooved similar to thegathering shoe 27a for maintaining the strands separate and in spacedrelation, the strands 28 are led around the idler wheel 33 and over andaround pull wheel 35. The strands are released from the pull wheel at amoving point reciprocating along an arc of the peripheral path of thewheel. This release is effected by the successive projection of fingers83 of the oscillating spoke wheel 39 located within the pull wheel 35,through slots 41 in the cylindrical surface of the wheel. The strandsare thus kinetically projected downwardly tangentially from the wheeland in a path moving back and forth across the conveyor 61.

The rear side of each pull wheel is covered by an independently mounted,oscillatable back plate 42 (see FIG. 3) on which the associated spokewheel is carried. Back plate 42 of the assembly including pull wheel 35is arcuately oscillated through a rearwardly projection post 43. Thelatter is driven by functioning of a fluid cylinder or other mechanism(not illustrated) which acts through the triangular link 45, whichpivots upon bar 47 mounted on the base 49 as shown in FIG. 2. The rodextending from the cylinder or other activating mechanism is joined tothe triangular link 45 by linking rod 46. The base 49 is positioned onthe platform 50 which also supports the other wheel 35, motors 38 andother equipment associated therewith. Platform 50 rests upon an operatorfloor 52.

Through the connecting assembly 55, including the turnbuckle 56, thetransverse movement of the triangular link 45 is transmitted to a post43 to also arcuately oscillate the back plate and spoke wheel 39 withinthe other pull wheel 35. With a single means effecting the oscillationof both spoke wheels their action may be closely synchronized.

The group of strands 58 thrown down by the pull wheels 35, 35, and thestrands from the pull wheels following this pair are accumulated in matform upon the traveling conveyor 61, which may be a carbon steel chainconstruction. Side shields 63 define the edges of the mat 60 and preventundesirable lateral overreaching of the strands.

The width of the conveyor covered by the mat in this case may be variedthrough a wide range by changing the oscillating arc length of the spokewheels and the distance of the pull wheels above the conveyor. The sideshields 63 are adjustably mounted so that their spacing may be alteredto match the desired width of the deposited material. For example, thewidth may be varied between limits of 14 inches to 84 inches.

The width of the pull wheels may be varied to accept a higher or a lowernumber of strands, the slots therethrough being made proportionatelylonger and the exterior portions of the fingers also madeproportionately wider. The movement of the fingers 83 into the slots 81and their momentary projection through the slots to release the strandsis synchronized through a timing drive between the pull wheel and thespoke wheel. This may include a toothed pulley fixed upon the hub of thepull wheel, a cog timing belt running between this pulley and a pulleyon a shaft upon which the spoke wheel is journaled.

The distance of the pull wheels above the conveyor, and the rotationalspeed of the wheels are so selected, in relation to the specificationsof the strands being deposited, that the strands are projected withsufficient force to carry them as a band of generally constant form andin substantially regular paths to the surface of the conveyor or othercollection surface. Each group of strands is thus deposited in areciprocating strip across the conveyor in a constant repeating patternand with substantially stable dimensions.

A larger range of relationships can be established between the stripslaid by various pull wheels in the system shown, but any one product maybe reproduced uniformly by locking the system into the dynamicrelationship which has been found to produce the particular matconstruction desired.

Referring to the sectional view of the mat produced as shown in FIG. 5it can be seen that the mat 60 incorporates upper and lower surfacelayers 80 of light strands and a central body portion 82 of heavierstrands. Since each bushing is supplying 438 filaments, the upper andlower layers 80 comprise two layers of 22 strands each from the firstand second bushings and two layers of 22 strands each from the last twobushings in the series of twelve bushings. The intermediate body portion82 includes eight layers of 14 strands each. As noted hereinbefore, thestrands in the upper and lower surface layers 80 contain approximately20 filaments per strand whereas the strands in the central body portion82 contain 29 to 31, or approximately 50 percent more, filaments perstrand. However, there are more strands per unit area in each of thesurface layers 80 than in the central body portion 82. Thus, the smallerstrands in the surface layers not only are able to lie more closelytogether to form smaller interstices because they are smaller indiameter, but there are more strands deposited per unit area so that agreat many more interstices are formed than in the central body portion.This enables better particle entrapment capabilities when the mesh sizeof the surface layers 80, particularly the upper surface layer 80, ischanged by the process to be hereinafter described.

As the mat 60 leaves the strand deposition position area, it isconducted through a binder application area. At a first liquidimpingement or flooding station 170, a liquid suspension material 174(preferably comprising solid binder particles suspended in a liquidstrand dispersing medium) is distributed evenly across the mat-likecollection of strands by a weir means 171. A supply line 172 suppliesliquid to the weir means 171 from a suspension mixing tank or sump 100via a pump 102. A valve 173 may be utilized to control the flow of theliquid suspension to the weir 171 and thus the amount of liquidimpinging upon and flooding the strands in the mat-like mass 60. Theliquid suspension 174 collects on a liquid retaining means, such as aplate 176, in a flood condition as noted at 175 to inundate the mat 60completely.

At end 177 of the liquid retaining means 176 may be opened to enable theflow of excess suspension material 174 into a collecting trough 190 atthe left side of the liquid retaining plate 176. Upwardly extending sidewalls or plates 178 are provided to prevent a flow transverse to thedirection of travel of the mat and the stream formed by the flooded area175. The side plates or walls 178 advantageously are spaced closely tothe edges of the mats 60 to prevent flow of the suspension material 174out through the edges of the mat. The prevention of edge flow willmaintain the dimensional qualities of the mat and will prevent anonuniform binder distribution in the edge areas. The side walls 178 maybe extended past the termination of the plate 176, as noted at the rightof plate 176 in FIG. 1, so that draining of the flood stream 175 fromthe mat 60 will occur only down through the mat rather than out throughthe edges thereof.

A flood stream flow will occur in the flooded area 175 if the liquidsuspension is provided at a rate to flood the mat 60 completely and tomove along therewith. A sufficient flow is advantageously provided byregulating the valve 173 so that the flooded area 175 will become astream moving at substantially the same rate and in the same directionas the mat 60. The strands in the mat 60 will therefore not be disturbedfrom the orientation provided by the deposition apparatus. A secondtrough or catch basis 191 at the right end of the liquid retaining plate176 catches the flood stream 175 as it drains down through the mat 60 asthe conveyor 61 and mat 60 pass the right end of the plate 176. Conduits192 and the pump 193 cooperate to return the suspension materialscollected in troughs 190 and 191 to the suspension mixing tank or sump100.

The length of the liquid retaining plate 176 and thus the intervalduring which the mat is maintained in the flooded condition isdetermined in response to the speed that the mat is moving through theflooded area and the soaking time necessary for the strand dispersingmedium in the suspension materials to overcome or substantially overcomethe forces holding the filaments together in strand form. The soakinginterval in the preferred embodiment is calculated or based upon theforces holding the smaller strands together that are lying in the uppersurface of the mat 60 since, as will be noted hereinafter, thedispersion of the strands in the upper layer 60 is a critical factor inchanging the mesh size to provide a higher binder percentage content inthe upper surface layer.

With some strands it may be possible through soaking alone to dispersethe strands in the upper layer before the strands disperse in theintermediate or central body portion of the mat 82, depending upon thenumber of filaments in the strands and the relative treatments providedwhen the strands of the upper layer and the central body portion areformed and deposited. But, the preferred and the most effectivedispersal of filaments of the strands in the upper layer in the mat 60may be accomplished by using a second liquid impingement station 180.

The second liquid impingement station 180 is spaced from the firstimpingement and flooding station 170 a distance, depending upon thespeed of the conveyor 61, which is adapted to provide a predeterminedsoaking or bond weakening interval. The second impingement stationincludes a weir 181 supplied via a supply line 182, the amount suppliedbeing controlled by a valve 183 connected between the pump 102 and theweir 181. If desired a second weir 185 may be interposed between thesupply line 182 and the weir 181 to provide a double weir constructionwhich will reduce turbulence when high flow rates are utilized.Apparatus for preventing or removing foam, such as bars placed acrossthe surface of the liquid suspension in the weirs 185, 181, may beutilized to prevent flow of foam into the flooded upper surface of themat 60 and an interference with the strand dispersing and binderdistribution operation being performed. Similarly, foam prevention orremoval apparatus may be used with the weir 171.

The control valve 183 in combination with the construction of theforward lip 186 of the weir 181 to provide a regulated, predeterminedforward velocity of the impinging stream 184 with respect to the mat 60and the flood stream 175. It is desirable to provide the impingingstream 184 with a slightly higher forward velocity vector than that ofthe flood stream 175 and the mat 60 for most effective strand dispersalin the upper layer.

A major portion of the excess suspension materials in the mat 60 isremoved by gravity drainage from the mat 60 into the collecting trough191 at the right of the liquid retaining plate 176 as the conveyor 61and mat 60 clear the end of the plate 176. Further excess liquidsuspension materials are removed from the mat 60 by passing theforaminous conveyor over a plurality of suction chambers 200, 210,having suction slots 201, 211 formed in the upper side thereof. A blowersystem 230 connected to the suction chambers 200, 210 by a conduit 220and via a separator unit 240 causes a reduced pressure in the chambers200, 210 and a positive flow of air downwardly through the mat 60 toextract excess liquid suspension materials therefrom. The separator unit240 separates liquid and particles that may be entrained in the airstream and diverts the suspension materials in the air stream anddiverts the suspension materials in the air stream to the retrivedsuspension storage tank 250. The cleaned air exits from the separator240 through an exhaust system 245. A pump 251 and a conduit 252 returnsthe retrieved suspension materials to the suspension mixing tank 100.

The powdered binder or binder particles are added to the liquid carrierat a rate equal to the rate of deposition of the binder particles fromthe suspension onto the mat. This may be accomplished by sensing thethroughput of the 12 bushings by a throughput measurement and controlunit 270. The control unit 270 may provide a signal on leads BM1 and BM2to a binder metering control unit 264 to regulate a binder feedingdevice 265 to control the amount of powdered binder put into the tank100 from a particle binder supply 260 to maintain the percentage ofbinder particles supplied to weirs 171 and 181 substantially constant.

The throughput measurement performed by the unit 270 is accomplished bysensing the amount of heat supplied to the bushings 21 to maintain themolten glass therein at a desired attenuating temperature. If the amountof fibers being attenuated is greater, then the heat requirements aregreater, and a measurement of the throughput of the bushings isobtained.

It is also desirable to control the line speed of the conveyor 61 sothat a uniform mat thickness is collected thereon. This may beaccomplished by providing signals on leads CS1 and CS2 from thethroughput measurement unit 270 to a conveyor speed control 267. Thissignal may be the same as or proportional to the signal applied on leadsBM1 and BM2 since the production of a greater amount of fibers shouldcause the conveyor speed to be greater to maintain a uniform thicknessof mat collection.

Since the rate of retention of binder particles by the mat-likecollection will depend upon the rate of fiber production and/or the rateof movement of the collection, signals representing the line speedcontrol 267 and applies to the binder metering control 264 via leads BM3and BM4.

The dispensing medium 90 in tank 100 is constantly agitated by a stirrer101 driven by a motor 104 to prevent the binder particles from settlingout. In addition an agitator 105 driven by a motor 106 is placedadjacent the point of initial contact of the binder particles with theliquid to promote a fast wetting of the solid binder particles. Thedispensing medium is provided from strand dispersing medium supply 110via a valve 111 to the binder mixing and agitation tank 100. To preventsettling out of the powdered binder or binder particles anywhere in thesystem, agitation is provided throughout the system by pumping largeamounts of the liquid suspension from the tank 100 through the binderapplication area in the closed loop system shown so that a high rate offlow in all of the conduits and associated apparatus will preventsettling or separation.

The flow of suspension material from the supply 110 is regulated by alevel control unit 268 which is responsive to the level in tank 100 asdetected by a probe 269, to regulate the opening and closing of thevalve 111. The unit 268 thus maintains a desired quantity or level intank 100.

As described, the mixing and application system is of the closed loopnature so that all materials are completely and efficiently used. Thereis no loss as a result of drainage, spillage, inefficient application,powder fall-out, dry powder fall-through, or air currents.

In summary, the binder application area includes a flooding weir 170 forapplying binder (solid binder particles in suspension) to the mat 60.The suspension stream 174 from the weir 171 preferably is flowedsubstantially vertically downwardly from the weir 171 to completelyinundate the mat. The fluid suspension strikes with sufficient force toflatten out all mole hills, tunnels, and like irregularities which causenon-uniformities and which may have occurred in the deposition of thestrands on the conveyor, but does not disturb the fiber orientation anddoes not affect mat uniformity. The no-load thickness of the mat isreduced by the flooding weir and the positive air flow therethroughduring suspension extraction.

A soaking section is provided after the flooding weir 170 where thecompletely submerged mat is allowed to move with a pool of binder andstrand dispersing medium at the same velocity so that all of the strandssoak for a predetermined interval. The soaking interval may vary withthe number of filaments in the strand, the type of forming size appliedto the strand, and other conditions. With the specifications set forthhereinafter for a preferred embodiment of this invention, it has beenfound that a soaking interval of as little as 7 seconds may besufficient.

The purpose of the soaking section is to break down any bonds or otherforces that may be holding filaments together in strand form in thelayer or layers that are to be filamentized. The excess binder andstrand dispersing medium flowing from both ends of the soaking sectionover the ends of the plate 176 is collected in the catch basings 190,191 and sent back to the sump mixing tank 100.

A dispersing weir applies and impinges more binder and strand dispersingmedium onto the top of the mat and the flood stream, after the soakinginterval had expired. The fluid preferably flows from the weir 181 sothat the horizontal vector of the impinging stream is substantiallygreater than the vertical vector thereof so that the impinging streamhas a slightly higher velocity than that of the flood stream 175 and themat 60 for most effective dispersing capability. The strands in theupper layer are therefore at least partially dispersed into theirindividual filaments to change the mesh size to a value which willmechanically entrap binder particles in the upper portion or surfacelayers.

In the preferred embodiment of the method, apparatus, and of the productbeing formed, this is accomplished by the combination of providingstrands in the upper layer which have fewer filaments per strand andthus are more readily reopened, and by providing more of the strands perunit area in the upper layer so that the interstices of the strands liecloser together. This combination encourages a rapid change in mesh sizeto retain or entrap the binder in the upper layer before a mesh sizechange occurs in the central body portion that would retain more bindertherein or substantially inhibit the flow of the binder particles out ofthe central body portion. Some binder is of course, desirably retainedin the central body portion of the mat, whether liquid and/orparticulate binder, by surface tackiness of strands and filaments in thecentral body portion and the lodging of the particles at the crossoversor intersections of the large strands, even though there are fewerstrands per unit area in the central body section.

Since the bottom layer is also composed of strands having fewerfilaments per strand, and since there are more strands per unit area,the soaking interval and the contact with the strand dispersal mediummay be adjusted to overcome the forces holding the filaments together instrand form before a similar reaction occurs in the central bodyportion. Then, as the water or dispersant is draining out of the mat 60into the catch basin 191 through the bottom layer, it is believed that ahole seeking flow may occur through the smaller interstices of thebottom layer which will cause at least a partial dispersement of thefilaments of the strands in the bottom layer by filaments being carriedtoward the holes by the flow. If a positive mechanical dispersing actionis desired, an array of nozzles or a slit nozzle may be provided acrossthe bottom of the plate 176 and connected to the sump 100 via a suitableflow regulator, to provide a flow which will impinge the lower surfaceof the mat 60 through the foraminous conveyor in the same fashion as theupper layer is dispersed. There may be thus created a mesh size changewhich may not, depending upon the number of filaments per strand and theforces holding the strands together, change the mesh size of the bottomlayer as much as the mesh size of the top layer is changed. All of thebinder particles therein or going therethrough because of the drainingaction may not be entrapped in the bottom layer.

Whether filamentized or not, the bottom layer at least providessubstantially more intersections to filter some binder out of thedraining flow from the central body portion and the bottom layer itself.Thus, there is a higher percentage binder content in the bottom layerthan there is in the central body portion, although the binder contentof the bottom layer may not be as high as that of the top layer. Thehigher binder content in the bottom layer will provide the mat withexcellent surface properties and enhance the handleability of the mat.

It can be seen ,then, that one of the major principles of the inventionlies in circulating binder uniformly throughout a mat-like mass, andthen selectively changing the binder retention capabilities of one ormore areas in the mat to enable the areas having a changed retentioncapability to have a higher binder content than the remaining areas ofthe mat. This is most effectively accomplished by insuring at least apartial positive dispersal of the strands, as taught hereinbefore withrespect to the top or upper layer of the mat 60.

Although discussed generally hereinbefore, it should be noted that thebinder particle content in the strand dispersing medium may besubstantially reduced and/or removed completely, while the liquid binderportion is substantially increased to obtain desired binder contentconcentrations. While there is no comparable mechanical entrapment ofbinder, the selective in-place filamentization of one or more layersafter the liquid binder has been thoroughly and uniformly distributedthroughout the mat will provide increased glass surface areas andintersections for receiving the liquid binder. Thus, the binderconcentration will be higher in the filamentized layer or layers than inthe remainder of the mat.

Because of the delicate nature of the control of the selectivefilamentization of a portion of the mat, it is preferred to providerelatively sharp distinctions between the binder retention capabilitiesof the layers wherein a binder concentration is desired and the otherlayers of the mat, as in the preferred embodiment disclosed herein, toreduce the responsibilities of the operators when the apparatus is on aproduction line. The product desired can then be obtained even thoughvariations occur during the production in the deposition of strands inthe application of forming size to the strands, in the diameters of thefilaments and the strands, in the composition of the binder, and/or inthe percent or type of binder particles suspended in the carrier.

However, the principles herein are applicable under controlledconditions without sharp distinctions being made between layers,particularly when a thicker mat is being produced. That is, thefilamentization and mesh change desired in the upper portion of the matmay be accomplished by impinging a mat composed of strands, all havingthe same characteristics throughout the thickness of the mat, anddesigning the final impinging stream supply for filament dispersal sothat only strands in the upper portion of the mat are affected anddispersed to change the mesh size thereof and to retain a higherconcentration of binder particles therein. As noted hereinbefore, therewould not be a sharp division between an upper portion or layer in thislatter instance and the lower portion, since the degree offilamentization of the upper portion would gradually decrease from theupper surface downwardly as the effect of the impingement streamdecreases, rather than having a relative sharp distinction between meshsize areas.

The binder application area also includes an extraction section whichremoves excess binder from the mat by first draining the liquid carrierand binder from the mat and then by passing air or other gas at arelatively high rate of flow through the mat for positive extraction. Inthe preferred embodiment of this invention the rate of flow of airthrough the mat is controlled so that the binder or liquid suspensionmaterial left in the mat, as the mat enters the oven, weighs about thesame as the strands and filaments in the mat. The preferred embodimentof the mat after curing has an overall binder content of about 31/2percent by weight, as obtained from an average of 5 percent in the upperlayer of the mat, about 11/2 to 2 percent in the central body portion,and between 11/2 and 4 percent in the lowermost surface of the mat. Thebinder and the air removed from the mat pass into a gas separator systemwhere the gas is removed and exhausted to the atmosphere while thebinder and dispersant is returned to the sump.

In the preferred embodiment the overall mat has approximately an 80 meshporosity so that binder particles of 100 mesh size or higher will tendto circulate or be distributed freely throughout the mat of the mass.When the mesh size of the mat is changed, as by the application of thefilament dispersing impingement stream 184 from the weir 181, the upperlayer of the mat surface changes mesh size so that its porosity is atleast 100 mesh thereby entrapping 100 mesh size particles in the upperlayer.

An electrical grade laminate reinforced with mats having the surfacewith higher binder percentages facing outwardly provides the laminatewith much better electrical characteristics. The higher binder particleconcentration in conjunction with the finely dispersed filaments in thepreferred embodiment apparently imparts higher or better dielectricstrength to the surface of the laminate.

When using the novel product of this invention as a reinforcement forproducts the following improvements over other commercially used matshave been noted. The wet-through of the impregnating material is muchfaster. The forming press may be closed at a faster rate. No specialpour pattern from the impregnating matrix is required. The higherporosity prevents dry spots or wash. The even horizontal binderdistribution avoids the occurrence of soft edges. The wet-out by theimpregnating matrix is better. There is less surface fiber prominence asa result of the finer strands. Heavily filled resins may be used. Whenthe reinforced product is used as circuit mounting boards, the laminateshave better punchability properties with less crazing and cracking inthe circuit board surfaces and interior. The lower overall bindercontent, as compared to past reinforcing mats similarly used, enablesthe provision of more reinforcing glass fibers per unit area in thefinal product. The lower binder content and the coarser strands in thecentral body portion improve the moldability of the mat.

As noted hereinbefore the surfaces of the novel product are more tightlybonded to provide an improved handleability. Surface defects such asmole hills, puff balls or tunnels are substantially eliminated. The edgeweight is more uniform. In addition, the compacting and elimination ofsurface defects and the other improved physical characteristics of themat product enables a better thickness control of the product made whenusing the mat as a reinforcement, for example when a relatively thinelectrical grade laminate is being formed. The standard powdered binderapplication method of the prior art can be used on mats with a weightrange of three-fourths of an ounce to 4 ounces per square foot. Thisinvention will extend the range of mat weights possible down toone-eighth ounce and up to 6 ounces per square foot.

The prior art mats which are not filamentized on the surface tend tocause a cracking or crazing when the reinforced product is beingpunched. Other prior art mats which are completely filamentized havedecreased porosity throughout the mat and presents matrix wet-outproblems in some applications. The present mat provides improved crazingresistance. This is believed due to higher binder concentration andgreater filament dispersion at the surface being punched.

In prior art mats difficulties have been encountered sometimes withbinder migration when the mat is being cured in an oven. In thepreferred embodiment of this invention, the mechanical entrapment of thebinder particles substantially reduces migration problems.

This improved mat may also be used advantageously in pultrusionapplications. It processes better than other continuous and choppedstrand mats in pultrusion applications due to better fiber bonding onmat surfaces and even compaction of the mat. It wets out and givesbetter laminate properties than chopped strand mats.

In conclusion, it is pointed out that while the illustrated examplesconstitute practical embodiments of out invention, we do not limitourselves to the exact details shown, since modification of thesedetails may be made withoup departing from the spirit and scope of thisinvention.

We claim:
 1. A method for selectively depositing binder in one layer ofa multi-layer mat-like mass, comprising the steps ofa. depositing aplurality of successive layers of multi-filament strands on a collectingsurface in a mat-like mass; b. distributing binder particles throughoutthe mat-like mass, the binder particles having a mesh size with respectto the mesh size of the layers which enables circulation of the binderparticles through the mat-like mass; c. opening the strands in one ofsaid layers to separate the filaments of the strands from each other andchange the mesh size of that layer to mechanically entrap more binderparticles therein; and d. removing excess binder particles from saidmat-like mass.
 2. A method for selectively distributing binder in amat-like collection of continuous filament strands, comprising the stepsofa. distributing binder particles throughout the mat-like collection ofstrands, the particles having a mesh size which enables distribution ofthe particles to all portions of the mat; b. opening the strands in oneportion of the mat-like collection to separate the filaments of thestrands from each other in said one portion to change the mesh size ofsaid one portion to a value which will entrap said binder particles insaid one portion; and c. removing at least part of the binder particlesfrom the remaining portion of said mat-like collection to provide amat-like collection having at least one portion which has a higherbinder content percentage than the rest of said mat-like collection. 3.A method as defined in claim 2 in whicha. the strands to be opened insaid one portion are formed with a faster reopening capability inresponse to contact with a strand dispersing medium than the strands inthe remainder of the mat-like collection, and in which b. said strandopening step includes flooding said mat-like collection with a stranddispersing medium to reopen the strands in said one portion, andremoving said strand dispersing medium from said mat-like collectionafter the strands in said one portion have reopened to change the meshsize of that portion and before the strands in the remainder of themat-like collection are reopened to entrap binder particles.
 4. A methodfor forming a mat from continuous glass filament strands wherein the mathas a controlled difference of binder distributed through the thicknessof the mat, comprisinga. delivering a first set of strands from a firstsource, delivering a second set of strands from a second source, thenumber of glass filaments in each strand of said first set differingfrom the number of glass filaments in each strand of said second set; b.successively collecting said first and second sets of strands on areceiving surface so that a layer-like mass of one set of strandsoverlies a layer-like mass of the other set of strands to form amat-like collection of strands on the receiving surface; c. floodingsaid mat-like collection on said receiving surface with a suspension ofbinder particles in a strand dispersing liquid carrier, the binderparticles having a mesh which enables the distribution of the binderparticles substantially uniform throughout the strands of bothlayer-like masses of said mat-like collection by the liquid carrierbefore strands start to open in response to contact with said stranddispersing liquid; d. soaking said mat-like collection in said liquidsuspension until the strands having the fewer number of filaments opensufficiently to change the mesh size of that layer to enable mechanicalentrapment of binder particles in that layer; and e. removing excessliquid suspension materials from said mat-like collection before thestrands in the other of said layers open to prevent passage of binderparticles out of said other layer.
 5. A method for selectivelydistributing binder in a mat-like collection of multi-filament strands,comprisinga. forming a plurality of sets of multi-filament strands, thefilaments of each strand in one of said sets of strands being gatheredin a strand form which enables strand reopening and filament separationmore quickly than strands in another set; b. successively depositingsaid sets of strands in a plurality of layers on a collecting surface toform a mat-like collection of superimposed layers; c. flooding saidmat-like collection with a suspension of binder particles in a stranddispersing liquid carrier, said binder particles having a mesh sizewhich enables distribution of the particles throughout the mat-likecollection by said liquid carrier; d. soaking said mat-like collectionin said liquid suspension to at least partially open said more quicklyreopened strands in said one layer to change the mesh size of that layerof strands to enable mechanical entrapment of binder particles in saidone layer; and e. draining liquid suspension materials from saidmat-like collection to remove excess liquid from said one layer whileleaving entrapped binder particles therein, and to remove excess liquidand binder particles from the rest of said mat-like collection beforestrands outside of said one layer open to prevent passage therethroughof binder particles to provide a mat-like collection having a firstlayer with a higher percentage and at least a second layer with a lowerpercentage by weight of binder particles therein.
 6. A method forproducing a continuous strand mat, comprisinga. continuously providing amat-like mass of multi-filament strands in an unwoven form on a movingsurface; b. flooding said mat-like mass on said moving surface with asuspension of binder particles in a strand dispersing liquid carrier byguiding said moving surface past a flooding suspension supply station,said binder particles having a mesh size which enables distribution ofsaid particles throughout said mat-like mass by said liquid carrier asthe mat-like mass is flooded; c. continuously adding liquid suspensionmaterials to said mat-like mass as it moves past said suspension supplystation at a rate to create stream flow in the same direction with andat substantially the same rate of movement as said mat-like mass on saidmoving surface; d. maintaining said mat-like mass in said flood streamof liquid suspension materials for a soaking interval sufficient toenable the strand dispersing liquid to substantially overcome the forcesholding the filaments together in strand form; e. impinging the floodedsurface and upper portion of said mat-like mass with a second supply ofsaid liquid suspension of binder particles at the end of said soakinginterval to disperse the filaments in the upper portion of said mat-likemass and change the mesh size of said upper portion of said mat-likemass to a value which mechanically entraps binder particles in the upperportion of said mat-like mass, said second supply impingement beingdistributed evenly across said moving mat-like mass and flood stream;and f. removing excess liquid and binder particles from said mat-likemass after impingement of the upper surface thereof and before thefilaments of the strands in the lower portion disperse to change themesh size of the lower portion to a value which would prevent binderparticle movement therethrough, thereby enabling the upper portion toretain a greater percentage of binder particles than the lower portionof said mat-like mass.
 7. A method as defined in claim 6 in which thestrands in the upper portion of said mat-like mass are formed with fewerfilaments per strand to enable a more rapid reopening than strandsadjacent to the upper portion.
 8. A method as defined in claim 7 inwhich more of the fewer filament strands are deposited in the upperportion of the mat-like mass in comparison to the number of strandshaving a larger number of filaments per strand in the mat-like massadjacent the upper portion, thus forming more smaller interstices in theupper portion enabling a more rapid mesh size change of the upperportion to provide a better particle entrapment capability.
 9. A methodas defined in claim 6 in which said multi-filament strands are glassfiber strands and in which said strand dispersing liquid carrierincludes a compound which provides a tacky coating for the filament andstrand surfaces to improve the binder particle retention capabilities ofthe filaments and strands in said mat-like mass.
 10. A method as definedin claim 9 wherein said compound providing the tacky coating is a waterdispersible resin or resin emulsion.
 11. A method as defined in claim 9in which:a. the filament diameters are approximately 68 to 70 hundredthousandths of an inch, b. the binder particles are 100 mesh size orsmaller; and c. the mat-like mass retains a total binder content ofapproximately one-half to 10 percent.
 12. A method as defined in claim 6in which the step of continuously providing a mat-like mass includesa.attenuating a plurality of filaments from molten streams of glass, b.forming multi-filament strands by gathering a relatively fewer number offilaments into strand form for deposit in said upper portion of saidmat-like mass, and c. forming milti-filament strands by gathering arelatively larger number of filaments into strand form for deposit insaid lower portion of said mat-like mass adjacent said upper portion.13. A method as defined in claim 12 which further includes the step ofdepositing more fewer number filament strands per unit area in the upperportion than larger number filament strands per unit area in saidmat-like mass adjacent said upper portion.
 14. A method as defined inclaim 6 in which said suspension removal step includes positivelyforcing air through said mat-like mass.
 15. A method as defined in claim6 which further includes the step of preventing flow out through theedges of the mat-like mass during the flooding and suspension removalsteps to maintain a substantially uniform binder distribution asachieved within the upper and lower portions of said mat-like mass. 16.A method as defined in claim 6 which further includes the step ofdimensionally controlling the width of said mat-like mass during theflooding and filament dispersion steps to prevent strand and filamentmovement transversely in response to edge flow of said suspension.
 17. Amethod as defined in claim 6 in which said suspension further includes aliquid resin for coating said strands and filaments in said mat-likemass and to enhance the binder particle retention capabilities of thefilaments and strand in said upper and lower portions of said mat-likemass by enabling some binder particles to be adhered to the filamentsand strands.
 18. A method as defined in claim 17 in which said liquidresin is selected from the group consisting of diethyleneglyco-fumarate, polyvinyl acetate, vinyl toluene, diacetone acrylimide,the reaction product of propylene glycol and maleic anhydride, and thereaction product of propylene glycol and trimellitic anyhdride.
 19. Amethod for producing a fibrous body from continuous glass fiber strands,comprisinga. continuously depositing a plurality of multi-filamentstrands in a mat-like mass on a moving surface including an upper layerin which the strands include fewer filaments per strand than the strandsin the next adjacent layer below the upper layer, said upper layerincluding more strands per unit area than said next adjacent lowerlayer; b. guiding said moving surface past a flooding station where saidmat-like mass is flooded with a suspension of binder particles in astrand dispersing liquid, said binder particles having a mesh sizeenabling distribution of the particles throughout the layers of themat-like mass, said flooding station adding said suspension at a rateand in a manner which creates a flood stream flow of said suspension inthe direction of movement of and at substantially the same rate ofmovement as said mat-like mass to inhibit movement of the floodedstrands with respect to each other; c. moving said mat-like mass alongin said flood stream of suspension materials for an interval sufficientto enable the strand dispersing liquid to overcome the forces holdingthe upper layer filaments together in strand form; d. impinging theflooded upper layer of said mat-like mass with a second stream of saidsuspension material to aid dispersement of the filaments in the upperlayer and reduce the mesh size of said upper layer to a value which willcause entrapment of said binder particles by said upper layer; and e.draining excess suspension materials downwardly through said mat-likemass after the change in mesh size of said upper layer and before achange in mesh size in the next adjacent lower layer which wouldsubstantially inhibit flow of binder particles in the lower layer, thepercentage of binder particles entrapped by said upper layer exceedingthe percentage of binder particles remaining in the next adjacent lowerlayer.
 20. A method as defined in claim 19 in which said draining stepfurther includes positively forcing air downwardly through said mat-likemass to reduce the suspension content in the mat-like mass below thevalue achieved by gravity flow of said liquid carrier.
 21. A method asdefined in claim 19 in which the step of continuously depositing strandsin said mat-like mass includes the deposition of a bottom layer in whichthe strands include fewer filaments per strand than the strands in thelayer which is adjacent to the upper layer and intermediate said upperand bottom layers, said bottom layer also including more strands perunit area than said intermediate layer.
 22. A method as defined in claim21 which further includes at least partially dispersing the lower layerfilaments to, in combination with the smaller interstices achieved bymore strands per unit area than the intermediate layer, cause the lowerlayer to provide a filtering effect during said suspension draining stepto catch at least part of the binder particles leaving the intermediatelayer, thus providing a mat-like mass having upper and lower layers witha higher binder content than an intermediate layer.
 23. A method asdefined in claim 22 in which the strand dispersing suspension furtherincludes a liquid binder for coating said strands and filaments in saidmat-like mass and to enhance the binder particle retention capabilitiesof the filaments and strands by enabling some binder particles to beadhered to the filaments and strands.